Polyarylene sulfide (hereinafter, also referred to as “PAS”), represented by polyphenylene sulfide (hereinafter, also referred to as “PPS”), is an engineering plastic having excellent heat resistance, chemical resistance, flame retardancy, mechanical strength, electrical characteristics, dimensional stability, and the like. The PAS has been widely used in a wide variety of fields of electric/electronic devices, devices for automobiles, and the like, because the PAS can be formed into various molded products, films, sheets, fibers, and the like by ordinary melt processing methods such as extrusion molding, injection molding, and compression molding.
As a representative method of producing PAS, a method in which a sulfur source and a dihalo aromatic compound such as p-dichlorobenzene, or the like (hereinafter, also referred to as “pDCB”) are subjected to a polymerization reaction in an organic amide solvent such as N-methyl-2-pyrrolidone, or the like (hereinafter, also referred to as “NMP”) has been known. As the sulfur source, a method in which an alkali metal sulfide formed by reacting mainly an alkali metal sulfide, an alkali metal hydrosulfide, and an alkali metal hydroxide in situ is used is also known. Furthermore, a method in which an alkali metal sulfide formed by reacting an alkali metal hydroxide and hydrogen sulfide is used as a raw material of a sulfur source is also known.
For a method of producing PAS in which a sulfur source and a dihalo aromatic compound are subjected to a polymerization reaction in an organic amide solvent under alkaline conditions, particularly in the presence of an alkali metal hydroxide, an attempt has been made to set conditions to stably perform the polymerization reaction and to suppress side reactions. That is, in this polymerization method, since an alkali metal hydroxide, such as sodium hydroxide (NaOH), or the like, is used at a high concentration during the polymerization reaction, the organic amide solvent is readily hydrolyzed by the alkali metal hydroxide and the decomposition product may be the cause of side reactions.
Patent Document 1 discloses a method of producing PAS, including: a preparation step of preparing a preparation mixture containing an organic amide solvent, a sulfur source, an alkali metal hydroxide, water, and a dihalo aromatic compound, and having a pH of 12.5 or higher; a first-stage polymerization step of heating the preparation mixture to a temperature of 170 to 270° C. to initiate a polymerization reaction, thereby forming a prepolymer having a dihalo aromatic compound conversion rate of 50% or greater; and a second-stage polymerization step of adding a phase separation agent into the reaction system containing the prepolymer and adding an alkali metal hydroxide in an amount corresponding to 1 to 10 mol % per 1 mol of the sulfur source at a time or in portions, thereby continuing the polymerization reaction at a temperature of 240 to 290° C. This method is a good method of producing PAS that stably and efficiently produces PAS having excellent reactivity with a silane coupling agent; however, further improvement has been demanded from the perspectives of yield of the PAS polymer, suppression of byproduct formation, and the like.
Therefore, as a method of producing PAS in which a sulfur source and a dihalo aromatic compound are subjected to polymerization reaction in an organic amide solvent under alkaline conditions, a method of producing PAS that can suppress side reactions caused by adding other alkali metal hydroxide and that can produce PAS having a high degree of polymerization at a high yield has been desired.